Python script to extrude with scale restriction
thanks batFINGER, your suggestion worked like a charm.  this is it:

    bpy.ops.object.mode_set(mode = 'EDIT')
    bpy.ops.mesh.extrude_region_move(MESH_OT_extrude_region={"mirror":False}, ...snip...
    bpy.ops.transform.resize(value=(1.5, 1.5, 1), constraint_axis=(False, False, False))
    bpy.ops.object.mode_set(mode = 'OBJECT')


with some magic numbers.